Recent data continue to indicate that DDT use may have adverse effects on human health, but essentially no findings on this topic have been replicated, so the question is still open. Whether DDT has adverse effects is important because DDT is still used for malaria control in 25 countries, alternative pest control strategies with less persistent agents are available, and current recommendations by the World Health Organization that support DDT use are based on the assumption that it has basically no adverse health consequences for humans. DDE is the major metabolite of DDT and is the best long-term biomarker of exposure. A previous study I did showed that DDE is associated with reduced birth weight; if this finding is replicated in a new study, this would constitute evidence that DDT use should be banned. Two previous studies suggest that higher exposure to DDE is associated with a shortended duration of lactation. Breast feeding prevents infant death. Therefore, DDT use may have the effect of increasing infant death. Additional information about this potential adverse effect is also needed. Mexico used the insecticide DDT for malaria control until 1999; many there in tropical areas have elevated blood levels of the DDT metabolite, DDE. My project in Mexico has two phases; both are based on the same group of subjects. I conducted phase 1 of this study: 1) To examine the relation between maternal serum levels of the DDE in relation to birthweight in 750 newborns in Tapachula, Mexico, and 2) to see if the antiandrogenic effect of DDE would decrease anogenital distance, which is a bioassay for fetal androgen action and a marker of reproductive toxicity. Phase 2 of this study will begin at the end of FY 2003. This study will follow the women and children enrolled in Phase 1, to determine if DDT exposure is related to reduced length of lactation among mothers. In addition, the offspring will be followed to examine early-life DDT exposure in relation to infection and growth. Last year's progress For phase 1, the number of subjects enrolled as of June 2003 was 671, thus the field team is on-target for the enrollment goal of 750, to be completed this fiscal year. The response rate has been 95%. Specimens for 250 subjects have been sent to a Canadian laboratory for analysis. Analysis of anthropometric data from the field team shows that the measurements are being done with reasonable reliability and that the measurement error is relatively small compared with the true variation among subjects. I visited the study coordinating center twice in the past year and the field center once. For phase 2, the final arrangements for the contract modification are still being completed.